1. Field of the Invention
The field of art to which this invention pertains is the reductive removal of a nitrogen oxide from a gaseous stream. More specifically, this invention relates to a catalyst useful for such reductive removal, methods of manufacturing that catalyst and the process in which the catalyst is used.
2. Background Information
The effective removal of a nitrogen oxide contained in gaseous streams, particularly waste streams, from various combustion systems has become an important task in view of heightened public awareness of the problems and effects of air pollution. In rising to this task, a wealth of art has recently been published dealing specifically with nitrogen oxide removal. Examples of these publications are: U.S. Pat. Nos. 4,048,112; 4,071,601; 4,085,193; 4,093,561; 4,096,096; 4,117,081; 4,119,568; 4,119,703; 4,131,643 and 4,138,469.
A common teaching throughout the above publications is that a nitrogen oxide may be reductively removed from a gaseous stream by contacting the stream with a reductant such as ammonia in the presence of a supported metallic catalyst. Following is a tabulation of the above publications and representative compositions of respective catalysts disclosed by each:
______________________________________ Publication U.S. Pat. No. Catalyst ______________________________________ 4,048,112 Vanadium oxide supported on the anatase form of titanium oxide. 4,071,601 Vanadium and tungsten oxide on an inorganic oxide support. 4,085,193 Titanium with possible metals including vanadium and tungsten on an inorganic oxide support. 4,131,643 The oxides of vanadium and niobium possibly with tungsten on an inorganic oxide support. ______________________________________
With further regard to U.S. Pat. No. 4,085,193, in Example X-4 thereof, a catalyst comprising oxides of titanium, tungsten and vanadium was prepared in a manner that resulted in a sulfuric acid radical to also be present in the finished catalyst composition.
The present invention comprises an effective catalyst useful for the reductive removal of nitrogen oxides from a gaseous stream, a method for making the catalyst and the reductive removal process for using the catalyst, all involving a unique step of acid treating the precursor of the catalyst which results in a novel catalyst composition.